This invention relates to a vehicle data acquisition system capable to sense, measure and store data on position, velocity and acceleration. In particular the invention relates to bicycle data acquisition systems and, in one non-limiting particular use, to bicycle motocross application.
Bicycle motocross (xe2x80x9cBMXxe2x80x9d) racing is a fast-paced sport in which the ability to accelerate quickly out of the starting gate and gain speed over the various obstacles is key to winning. Top BMX professionals have the ability to accelerate from 0 to 30 miles per hour in 60 feet. In many racing formats, a single race can last only 40 to 50 seconds. In this short time, multiple riders will start from a starting gate and traverse straight sections, banked curves, and obstacles. For instance, a race may involve 4 or 5 straightways, approximately 200 feet each in length, with straightways connected by banked turns, 60 to 80 feet in diameter, each straightway containing a variety of jumps, ranging from small, 2 feet high xe2x80x9cspeed bumpsxe2x80x9d to tall, 6 feet high double jumps in which riders can jump distances of thirty feet or more before landing. In these quick races with constant opportunity for mishap, one basic strategy is to get out in front of the other riders quickly and maintain position in order to reach the finish line first. A BMX bicycle is simplistic. Typically, the bicycle uses 20xe2x80x3 diameter wheels, has one brake, and has a single gear ratio with a freewheel hub. The use of variable gears is allowed, but is not prevalent The bicycle typically weighs about 25 pounds, with a frame made of steel or aluminum. The components of the bicycle are mostly aluminum.
A data acquisition system suitable for assessing BMX racing performance must be able to resolve position from the starting gate within a fraction of an inch. For example, a 3 inch difference between two riders at any point during a sprint would be considered significant. To track subtle changes in performance, the maximum acceptable error would need to be limited to a small percentage of this distance, perhaps 1% or 0.03 inches. Of course, for a wheel that produces only one data point per revolution, as is typical of conventional systems, the position from the starting gate could only be determined within one wheel circumference or less. For a 20 inch wheel on a BMX bicycle, this translates into about 63 inches.
BMX racing is very different from other cycling disciplines. In addition to being able to accelerate quickly, a great deal of handling skills, skills akin to those of handling motorized motocross motorcycles, are required to negotiate a BMX race course. Riders strive to pedal as much as possible in between the jumps and corners, and if possible, will attempt to pedal over certain obstacles without hesitation. Riders strive to stay on the ground and jump as low as possible to save time. The riders also have the ability to xe2x80x9cpump,xe2x80x9d or gain speed without pedaling by properly channeling their bodily momentum upon landing and over the various obstacles. The ability to pump can allow riders to greatly accelerate over sections of track where pedaling would be nearly impossible.
As with any athletic endeavor, the ability to accurately measure performance is the key to improvement. Two main performance measures in BMX racing are (1) acceleration out of the starting gate and corners, and (2) acceleration and/or conservation of momentum over the various obstacles. There has been no system designed specifically to measure these parameters for BMX performance assessment. Existing systems lack the required resolution to measure these quantities with sufficient accuracy to assist the rider in performance improvement.
Conventional cycling computers have the capability to record distance, crank speed and velocity. These systems typically use two single magnets, one on the wheel and one on the crank arm of the bicycle, to measure and display information for wheel and crank speed. These units also have the ability to compute average and maximum values over time. Conventional cycling computer systems do not provide adequate feedback for assessing BMX riding performance because they do not sample data with sufficient resolution.
There are a few systems that are significantly more advanced than conventional cycling computers. These systems were designed for road and track bike applications and not BMX applications. One system is produced by Schobere Rad Messtechnik (hereinafter xe2x80x9cSRMxe2x80x9d) of Kxc3x6nigskamp, Germany, which uses a strain-gage instrumented crank set to measure pedaling power. Data can be recorded at frequencies of 200 Hz. Wheel and crank position are measured using magnetic pulse switches, one sample per revolution, akin to conventional cycling computers. SRM provides an on-board computer (with telemetry option) to record detailed pedaling information. The SRM software then plots the data to show power output over time. It also performs calculations to assess pedaling efficiency/left-right leg output comparisons. The second example is the xe2x80x9cPower-Tapxe2x80x9d system, produced by Graber Products, Inc., of Wisconsin. The Power-Tap system is similar to the SRM system in that it records power output, only this time using an instrumented hub. Wheel and crank position are measured using pulse switches, one sample per revolution. This is similar to conventional cycling computers. The Power-Tap system has a slower sampling rate, providing a maximum sampling rate of one Hertz (Hz). Power-Tap recently issued a hub that will fit into a BMX frame.
While the advanced cycling computers described above offer distinct advantages over conventional systems, such as by having a higher sampling rate, they still do not provide a means by which detailed position versus time data can be obtained. Both systems still use the conventional magnet system that triggers only once per wheel revolution.
Even though BMX racers are very quick and powerful, the measurement of power output is a concept more relevant to road and track (velodrome) cycling than BMX racing. These cycling efforts take place over much larger distances than those encountered on a BMX bike. These bicycles are also geared much higher than BMX bicycles. BMX bikes are geared to xe2x80x9ctop outxe2x80x9d in approximately 150 ft or xc2xe of a straightaway, whereas a track rider will need to last several laps on a 333 meter track. One method by which road and track riders assess their fitness is by using relationships between heart rate and power output. The short duration of BMX races make these types of studies less meaningful, especially on short sprints, due to the lag time between exertion and heart rate elevation.
More importantly, the dynamics of BMX and track bike sprinting are very different from each other. Track bikes are closely sized to fit the rider. The bicycle""s movement is mostly a function of leg movement. A BMX sprinter is a different case. In BMX, a rider has many degrees of freedom in regard to pedaling stance/form because they do not sit down and the seat is not close to the rider. Add in jumps with quickly changing surface angles, and the meaning of power, as well as its translation into how quickly a rider moves from point to point, becomes nebulous. While power measurement may be useful for comparative purposes in BMX training, or for analyzing some aspects of pedaling efficiency, it just does not sufficiently quantify all the variables that define how fast a rider is moving.
Most importantly, one should note that some of the greatest periods of acceleration on a BMX bike occur when essentially no power is being transferred through the drive chain (hub and/or crank) of the bicycle. One example is the weight of the rider being thrust forward at the start. This acceleration comes mainly from the momentum of the upper body, and is not fully transmitted to the drive chain until the 3rd or 4th pedal stroke. Another example is a rider xe2x80x9cpumpingxe2x80x9d through a series of jumps without pedaling. Significant acceleration (enough to pass another rider on the track) can be obtained without rotating the crank set or loading the hub. In short, measurement of power does not sufficiently answer the most basic question of BMX performance assessment: how fast is a rider going from point A to point B?
What is needed is a method and apparatus to assist a bicycle rider to assess acceleration out of a starting gate and corners of a race track, and acceleration and/or conservation of momentum over obstacles.
The two performance measures of (1) acceleration out of a starting gate and corners of a race track, and (2) acceleration and/or conservation of momentum over obstacles are obtained through use of the present invention. An object of the present invention is to provide a bicycle instrumented with a data acquisition system to record detailed position versus time data. This data could then be manipulated to generate useful position, velocity, and acceleration curves with which to assess rider performance.